Program controls, especially those used in the appliance industry, typically include a control section which receives user input via a user-actuated knob coupled through a control shaft. The technology utilized for the control mechanism varies depending upon the cost and sophistication of the particular application, and may include cam operated timers or electronic controls. A common feature of these control mechanisms however, is that they operate based upon a rotational position of a control shaft through which a user selects the particular cycle desired. A familiar application of such controls is in a typical washer or dryer used in home and industry.
One of the most common user interfaces utilized in the appliance industry is the push/pull control interface. This popular control interface utilizes a user actuated control knob coupled to the control shaft of the program control. The various cycles available are selected by the user by pushes the control knob inward followed by a rotation thereof to the desired program cycle as displayed to the user on the front control panel of a typical washer or dryer. Once the user control knob has been rotated to the appropriate position as typically indicated by a selector line on the control knob, the user then pulls the control knob outward to begin the selected program cycle. If, at any point during the operation of the appliance, the user decides to terminate the current cycle, the user simply pushes in on the control knob to interrupt the operation of the appliance.
As can be well imagined, there must be some mechanism to hold the user interface control knob onto the control shaft to allow for proper operation of the controller without having the control knob pulled off the control shaft. This mechanism must also allow for the control knob to be moved from the control shaft to accommodate removal of the appliance control from the control panel in the event of failure thereof. While a control panel could include a hole of suitable diameter to allow the control knob to be pulled therethrough, such does not present an aesthetically desirable configuration. Therefore, a typical appliance includes a small hole through the front control panel of a size sufficient only to accommodate the control shaft itself, and not the much larger control knob. The primary mechanism for holding the control knob on the control shaft is a simple friction fit between the outer diameter of the control shaft and the inner diameter of the control knob. In this way, the unit is assembled by forcing the control knob on the end of the control shaft once assembled in the control panel of the appliance. Obviously, the force of friction holding the control knob on the control shaft must be greater than the force required to be applied by a user in pulling the knob outward to interrupt a current cycle or allow for selection of a new cycle during normal operation. With this friction fit it is still possible to remove the control knob from the control shaft to allow for servicing or replacement of the appliance control by applying sufficient force to overcome the force of friction holding the knob thereon.
A problem exists with this design however, in that, over time, the fit between the outer diameter of the control shaft and the inner diameter of the control knob becomes worn. Once this begins to happen, pulling of the control knob to interrupt the current cycle tends to also remove the control knob from the end of the control shaft. While this situation is initially only a slight inconvenience for a user requiring only that he force the control knob back on the control shaft, once this process has been repeated a few times the inner diameter of the control knob becomes more and more worn to the point where pulling on the control knob no longer actuates the control shaft to interrupt the current cycle. Once this occurs, the consumer is forced to either replace the controller, the knob, or utilize a pair of pliers or other mechanism to properly actuate the control shaft. While all of the above are workable solutions to this problem, the increased cost and aggravation associated with the primary user interface tends to deteriorate the appliance manufacturer's reputation in the market and destroys product loyalty as dissatisfied consumers voice their discontent.
In an attempt to overcome this problem associated with a friction fit between the control knob and the control shaft of a program controller for an appliance, many of the plant manufacturers are now utilizing a more active mechanism to retain the control knob on the control shaft once the controller has been mounted on the appliances control panel. While a snap fit or other locking mechanism could be appropriate to overcome this problem, the serviceability requirements of the controller on a consumer appliance requires that the control knob be removable for service without damage to either the control shaft or the control knob. To accommodate this serviceability requirement, many control shafts are now being designed with flexible cantilevers at the end of the control shaft which have locking barbs on the end thereof which securely engage a recess in the inner diameter of the control knob. As the control knob is slid onto the end of the control shaft, the flexible detents deflect inwardly until the recess on the inner diameter of the control knob is reached at which point the cantilevers are allowed to flex to their normal position with their locking barbs engaging this recess. Once the knob has been inserted on the end of the control shaft, a locking pin is inserted through the control shaft to come to rest between the flexible cantilevers to prevent their deflection inwardly, thus preventing the control knob from being removed from the end of the control shaft without the use of excessive force to a degree resulting in damage of the control knob, control shaft, or both.
One such control shaft is illustrated in U.S. Pat. No. 5,684,281 issued to Amonett on Nov. 4, 1997, for a TIMER CAMSTACK AND CLUTCH. In this design, a shaft locking pin is inserted through the hollow control shaft to be positioned between the two flexible cantilevers to prevent their inward deflection to retain the control knob positioned on the end thereof. The locking pin is held in place by a locking pin groove situated on the end of the locking pin which then engages two ribs on the inner surface of the flexible cantilevers. However, this design suffers from problems which makes its utilization in consumer and commercial appliance applications disadvantageous.
First, because the flexible cantilevers must include a rib on the inner surface to engage the locking pin groove, insertion of the locking pin must necessarily deflect the cantilevers in an outward direction upon insertion of the locking pin. To accommodate such outward deflection until the locking pin groove engages the ribs, the inner diameter of the user control knob must necessarily be slightly larger than would be necessary to accommodate the outer diameter of the cantilevers. This results in some unnecessary play in the fit of the control knob on the control shaft giving the impression of substandard quality. Alternatively, if the inner diameter of the control knob is made to fit more solidly on the end of the control shaft, the insertion of the locking pin will result in damage or at least increased wear on the ribs on the inner surface of the cantilevers, as well as on the end of the locking pin itself. Such wear will ultimately result in failure of the ribs and an inability to lock the control knob in place.
A second significant problem exists with this design related to the securing of the locking pin within the cantilevers of the control shaft. Specifically, since the insertion of the locking pin between the cantilevers having the rib on the inner surface thereof must result in an outward deflection of these cantilevers, an assembler may well believe that the increase resistance to the insertion of the locking pin is a result of the pin being locked in place. If this is assumed by an assembler, it is simply a matter of time before the inward force on the cantilevers by the control knob will work the locking pin far enough from the ends of the cantilevers that the control knob will eventually be pulled off by a user attempting to interrupt a cycle in progress or otherwise manipulating the control knob. In this situation, unlike the older style friction fit, reapplication of the control knob will not allow proper operation, as the cantilevers will easily flex to allow the control knob to be removed from the shaft.
Since the consumer has no way of reinserting the locking pin into the secured position in the control shaft, the consumer will be forced to request a service call. The requirement for a service call stems from the design of the locking pin which is freely inserted and removed from the back of the assembled appliance control. Since the assembled appliance control is installed on the reverse side of the appliance control panel, a service repair person will be required to remove the appliance control panel to simply reinsert the locking pin in place once the control knob has been reinserted on the control shaft. Considering that a typical service call costs between $50.00 and $100.00 at today's going rate, the profitability of an appliance incorporating such a design when the service calls are taken into account falls to an unacceptably low level. Likewise, the cost of ownership for a consumer, in view of the cost of a service call to replace a simple locking pin, becomes unacceptably high after the first such event. Even if a consumer learns how to remove the front control panel, reset the locking pin, and replace the control panel without inadvertently pinching or disconnecting any control wiring, the shear hassle involved in removing and replacing the front control panel from a consumer appliance, not to mention the safety risk associated with an untrained consumer removing the front control panel from an electrical device, will greatly decrease consumer loyalty and the manufacturer's reputation in the market place. As a result, this design is unacceptable from reliability and cost of ownership stand point, as well as from of a perceived quality and reputation stand point.
There continues to exist a need for a retaining mechanism for user control knobs for push/pull type controllers which will adequately retain the user control knob during normal operation of the control mechanism, and which allows for easy user replacement of the control knob should it become disengaged from the control shaft without the necessity of a service call or removal of the front control panel of an appliance.